This invention relates to a lock mechanism for an aircraft engine thrust reverser, particularly a lock mechanism which can form part of the drive train of a thrust reverser actuator.
An aircraft engine""s thrust reverser must only be deployed when the aircraft has landed. In order to avoid premature or other inadvertent deployment of the thrust reverser a locking system is provided for locking the thrust reverser cowl or other thrust reverser element in a stowed position. Part of the locking system can be a lock which prevents operation of the thrust reverser actuating mechanism. Our U.S. Pat. No. 6,138,449 discloses an hydraulically operated lock mechanism for locking an aircraft engine thrust reverser actuating mechanism against operation. The lock mechanism of FIG. 1 of U.S. Pat. No. 6,138,449 has, as shown in FIGS. 1 and 2 hereto, a shaft 12 which, in order to operate the thrust reverser actuating mechanism, is rotated at speeds up to 6,000 revolutions per minute by a prime mover, which, in the case of the mechanism illustrated in U.S. Pat. No. 6,138,449, will be an hydraulic motor. The shaft 12 can be locked against movement by first and second pins 15 which are spring urged to a position in which they obstruct the path of rotation of a plurality of radial arms 14 carried by the shaft 12. When it is safe and appropriate to actuate the thrust reverser mechanism of the engine the pins 15 are retracted hydraulically so that they do not obstruct the arms 14 and the shaft 12 can thus rotate.
A potential problem of the mechanism described in U.S. Pat. No. 6,138,449, but which is extremely unlikely to arise in use, is that if the hydraulic supply to the retraction mechanism of the pins 15 fails then the pins 15 can be driven forward at a time when the shaft 12 is rotating at up to 6,000 revolutions per minute. If this happens then firstly there is a risk that the pins and/or the arms 14 will be irreparably damaged, and secondly there is a possibility that the shaft 12 will be arrested during rotation while deploying or stowing the thrust reverser mechanism. The possibility of such an interruption in the hydraulic supply to the retraction mechanism of the pins 15 is extremely remote.
There is currently a requirement for electrically operated thrust reverser systems, and accordingly for electrically operated locking mechanism associated with such thrust reverser systems. It is a requirement of the lock mechanism that it is operable to lock the thrust reverser in a stowed position until released by an electrical signal, and thereafter, irrespective of interruption of the electrical energisation, the locking mechanism must not be rendered operative unless the thrust reverser mechanism has been returned to its fully stowed condition. It will be recognised that in order to produce an electrically operated version of the lock mechanism illustrated in U.S. Pat. No. 6,138,449 it would be possible, at least in theory, to replace the hydraulic retraction mechanism of the pins 15 by an electromagnetic retraction mechanism. However, in the theoretical electrical version of the arrangement illustrated in 6,138,449 it is recognised that the risk of inadvertent momentary interruption of an electrical supply to an electromagnetic retraction mechanism is somewhat greater than the risk of a dangerous interruption in the hydraulic supply. In solving this difficulty the inventors have produced an arrangement which is suitable for use with electrical or hydraulic operation and accordingly it is an object of the present invention to provide a lock mechanism for a thrust reverser which cannot be actuated by inadvertent interruption of the supply of either electrical or hydraulic power.
In accordance with the present invention there is provided a thrust reverser actuator lock mechanism comprising a rotatable shaft, rotation of which in one direction from a rest position drives an associated thrust reverser from a stowed position towards an operative position in use, retractable abutment means having a rest position abutting an element rotatable with the shaft to prevent rotation of the shaft, resilient means urging said abutment means to said rest position, and, mechanical latch means sensitive to the speed of rotation of said shaft for latching said abutment means in a retracted position against the action of said resilient means when the rotational speed of said shaft exceeds a predetermined value.
Preferably said mechanical latch means co-operate with said abutment means in such a manner that when said latch means latches said abutment means in said retracted position the abutment means must be retracted beyond said latched position and the speed of rotation of the shaft must be below said predetermined value in order for the latch means to cease to be operative so that the abutment means can move to its rest position.
Conveniently the mechanism includes electromagnetic retraction means for retracting said abutment means from said rest position.
Alternatively said retraction means is hydraulically actuated.
Desirably said latch mechanism is a centrifugal mechanism.
Conveniently said centrifugal mechanism extends within a sleeve movable axially relative to said shaft to retract said abutment means.
Preferably said centrifugal mechanism coacts with said sleeve to latch said sleeve in said retracted position.
Preferably said latch mechanism includes at least one bell-crank lever pivotally mounted on said shaft, one limb of said lever swinging radially outwardly of said shaft as said shaft rotates.
Desirably the other limb of said lever is received in a radial recess in said shaft.
Conveniently at least one further bell-crank lever is provided angularly spaced from the first mentioned lever about the axis of said shaft.
Preferably said shaft houses resilient means acting on the or each bell-crank lever to oppose movement of said lever under centrifugal force.
Desirably the free end region of said one limb of the or each bell-crank lever coacts with said sleeve in its retracted position when the rotational speed of said shaft has exceeded a predetermined value, to latch said sleeve in its retracted position.
Conveniently said sleeve carries an annular bearing encircling said shaft and the or each bell-crank lever engages the inner race of said bearing to latch the sleeve in its retracted position.
Preferably a generally radially outwardly extending shoulder of the or each bell-crank lever is engageable with a corresponding radial surface at the end of said inner race and shoulder and/or said surface are undercut so that under the action of said resilient means urging the abutment means to said rest position a self locking action is generated at said shoulder and said surface resisting return of the or each bell-crank lever under the action of said resilient means acting on the or each bell-crank lever.
Desirably in the inoperative position of said centrifugal mechanism a radial clearance exists between the inner surface of said sleeve and said mechanism to permit free axial movement of the sleeve relative to said shaft.
Conveniently said sleeve is the movable armature of an electromagnet.
Alternatively said sleeve is a movable piston of an hydraulic actuator.